Thursday, October 28, 2010

Army of Microscopic Life Probed for Health of Planet's Soil

Bijal P. TrivediNational Geographic Today

March 4, 2002

Diana Wall stands in her garden surrounded by bizarre and savage animals
that are eating, chewing, tearing, and grinding the dead plants around
her. Some have six legs; others, armor-like shells, bristly bodies, or
large, multifaceted ruby eyes.

A soil ecologist at Colorado State University in Fort Collins, Wall is fascinated with the creatures that facilitate rotting by breaking down plant litter, enabling the nutrients to be recycled for use by other organisms. Now she is part of an international effort to identify and name all the critters like these in 20 countries.

The project, called the Global Litter Invertebrate Decomposition Experiment (GLIDE), is part of the International Biodiversity Observation Year, now underway. The aim of GLIDE is to improve understanding of how the various species in different types of soilmites, nematodes, millipedes, and otherscontribute to rates of decomposition.

Such knowledge is important because the armies of microscopic creatures that live in the soil help it maintain its fertility, its porous structurewhich is essential for filtering waterand its role in Earth's cycling of carbon and nitrogen.

"For so long, anything underground was this big black box and, with the exception of farmers, very few people were interested in the organisms in the soil," said Wall. Now, because human activities are changing the natural systems of the planet dramatically, it's crucial to learn whether essential forms of biodiversity are being lost, she explained.

Picturing Decomposition

Wall and an international team of scientists are conducting experiments to determine what organisms participate in the decomposition process under various conditions and at different sites.

Wall's team at CSU put identical piles of alfalfa grass into more than 2,000 mesh bags, then mailed the bags to ecologists in 20 countries. The bags were placed in a total of 30 different ecosystems; for example, in the hot Namibian desert, humid oceanic broadleaf forests of Tasmania, temperate fields of Poland, and semiarid scrub plains of the United States.

Soil consists in large part of decomposed surface litter, said Wall. By placing these mesh bags filled with litter in different environments we can get a good sampling of the diverse fauna that crawls from the soil to break it down.

"We want to know whether the same organisms are chowing down on [the alfalfa]," said Mark Dangerfield, director of the Key Center for Biodiversity and Bioresources at Macquarie University in Sydney, Australia.

The scientists collected the bags several months later and measured the amount of rotting that had occurred. The tiny organisms were then extracted from the partially decomposed litter and collected in bar-coded vials and mailed to a laboratory in Australia.